The use of balloon catheters to treat strictures, stenoses, or narrowings within various parts of the human body is well known and is the subject of many patents. For example, GrUntzig, U.S. Pat. No. 4,195,637, Simpson and Robert, U.S. Pat. No. 4,323,071, Bonzel, U.S. Pat. No. 4,762,129, Yock, U.S. Pat. Nos. 5,040,548 and 5,061,273, Frisbee and Samson, U.S. Pat. Nos. 4,573,470 and 4,619,262, Chin et al., U.S. Pat. No. 4,493,711, Mueller et al., U.S. Pat. No. 4,790,315, Walinsky, U.S. Pat. Nos. 4,641,649 and 4,643,186, and others, teach that balloon catheters can be used to dilate stenoses in blood vessels. In each design, the balloon has a generally cylindrical shape, positioned in a concentric manner in relation to the catheter shaft, and bonded distally and/or proximally to the shaft. When an operator attempts to pass a dilatation balloon having such a design through a very tight opening in a stenosis, the balloon may bunch up, i.e., fold up longitudinally like an accordion, as shown in FIG. 1, and the catheter will not pass through the stenosis. A balloon catheter in which the balloon is bonded to the shaft for its entire length would eliminate this problem.
Inflation of a concentrically mounted balloon results in a uniform force circumferentially applied to the stenotic lesion. However, the structure or morphology of the lesion is rarely uniform, and harder portions will require more force to dilate than will softer areas. This has necessitated the practice of inflating the balloon at very high pressures, causing overdistention, dissection, and tearing. In addition, at high pressures, a dilatation balloon may rupture, resulting in serious complications. Thus, there is a need for a balloon catheter which can apply a focused, variable force for dilatation, at lower pressures.
In prior art dilatation balloon catheters, the shaft segment within the balloon may be a solid wire (Frisbee and Samson), or it may be a hollow and open-ended tube which allows the catheter to be moved over a guidewire (Simpson/Robert, Bonzel, Yock). The catheter of Mueller et al., a representative structure of which is shown in FIG. 2, has small holes in the shaft proximal to the balloon to allow blood to enter, for the intended purpose of allowing blood to perfuse the vessel while the balloon is inflated. Since the blood impacts the balloon, turns to enter the small holes in the shaft, and then turns again to exit the catheter in the proximal direction, this design promotes iturbulent blood flow of the type that often results in hemolysis and thrombosis. The balloon of Walinsky is porous and is intended to deliver a therapeutic agent to the lesion while the balloon is inflated. Since the inflation pressure of the balloon is often high to effect dilatation, the drug may exit the pores in the balloon at a velocity that would injure or even perforate the vessel.
Thus, there is a need for a balloon dilatation catheter with a lumen positioned external to the balloon, such that the lumen could be used for therapeutic means (e.g., blood perfusion, drug delivery) during balloon inflation.